Depth Resolution in Dynamic Near-Infrared Spectroscopy of the Human Brain
spectroscopy (NIRS) non-invasively monitors brain activity in human subjects, and cyclic
thigh cuff inflation is one way of inducing coherent oscillation of oxy-, deoxy-, and
total hemoglobin concentrations in brain tissue. Based on the frequency-resolved study
of induced hemodynamic oscillations in human tissue, a novel approach called coherent
hemodynamics spectroscopy ... read more(CHS) is introduced by our group. In CHS, the phase and
amplitude spectra of hemodynamic oscillations can be translated into physiological
parameters such as capillary transit time and cerebral autoregulation cut off frequency.
However, the modified Beer-Lambert law, a typical method in NIRS to calculate
oscillations of hemoglobin concentrations, is based on an assumption that hemodynamics
is homogeneous in brain, which does not discriminate hemodynamics in the scalp from the
cerebral layer. In this paper, we introduce a new model which enables us to measure
absolute values of hemoglobin concentration in cerebral and extracerebral tissue of
human brain, and thickness of extracerebral layer. This method features a direct
solution to coefficients of two-layered media and the thickness of the top layer, based
on diffusion theory and an inversion procedure based on the Levenberg-Marquardt
algorithm. To our knowledge, this is the first time that coherent oscillations in brain
can be measured in scalp and brain cortex separately with no other prior
Thesis (M.S.)--Tufts University, 2016.
Submitted to the Dept. of Biomedical Engineering.
Advisor: Fantini Sergio.
Committee: Irene Georgakoudi, and Brian H. Tracey.
Keyword: Biomedical engineering.read less
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